Many enterprise networks are replacing their existing Private Branch Exchange (PBX)- and Central Office Exchange (CENTREX)-based telephony systems with systems based upon Voice-over-IP (VoIP) and Session Initiation Protocol (SIP)-based signaling systems that utilize the existing enterprise IP infrastructure, e.g., Local Area Network (LAN) and Wireless LAN (WLAN) technologies. It is not uncommon for enterprise employees to regularly use mobile communications devices when away from the enterprise, which interoperate with cellular networks such as, e.g., the Global System for Mobile Communications (GSM) networks, Code Division Multiple Access (CDMA) networks, and Universal Mobile Telecommunications System (UMTS) networks, to keep in touch with other employees of the enterprise and to conduct business communications with other people outside the enterprise. Additionally, mobile communications devices are being enhanced to provide SIP-based communications (including VoIP) over WLAN access as well as cellular networks, thereby allowing these devices to provide mobile telephony communications capability when within the enterprise as well as when away from the enterprise. It is expected that such developments may allow replacement of the ubiquitous wired desktop phone in the enterprise with dual-mode, WLAN-capable mobile devices.
Although cellular telephony networks have deployed IP-based data communications capabilities through exploitation of well-known technologies, it is generally understood that these networks cannot currently commercially support carrier-class VoIP telephony services due to issues of delay, Quality of Service (QoS) and efficiency, which prevent cost-effective usage of such networks for purposes of providing acceptable quality voice services. Accordingly, for the foreseeable future, telephony services based upon the existing network infrastructure are likely to continue to utilize conventional circuit-switched network technology for telephony calls.
Based on the foregoing, it should appreciated that the integration of VoIP enterprise networks with carrier cellular telephony networks in order to serve an enterprise user within the enterprise as well as while away is fraught with numerous difficulties. Moreover, in such scenarios it may be desirable for enterprises to have certain control over the calls made by their employees for tracking and monitoring purposes. In addition, it would be desirable to provide value-added enterprise call integration services within the context of ongoing development of current 3rd Generation Partnership Project (3GPP) standards which specify an Internet Protocol (IP)-based core network architecture referred to as the IP Multimedia Subsystem (IMS).